Phase Cancellation

[raab]

Can somebody explain what phase cancellation is? I can't wrap my brain around the concept!!!

[bennychico11]

think of two sine waves for example with the exact same amplitude. if they both start at the exact same time they will be in sync. when one part of the wave goes above the zero crossing, the other one will too....and when it goes below the zero crossing, the other will too.

now, take that second wave form and move it a half of a cycle either way so that when the first sine wave arcs up over the zero crossing, the other one arcs DOWN over the crossing. this is said to be 180 degrees out of phase and will result in cancelling eachother out so that you hear nothing. now, there's also vary degrees of phase cancellation that can cause annoying problems when recording instruments with two mics. have you ever heard of a weird flanging effect when listening to overheads or other instruments that were miced w/ two mics? that's phase cancellation. in the normal world you rarely hear exactly 180 degree of cancellation because we work with complex waves...not sine waves. so every once and awhile you get something a little bit out of phase and then it will go back in phase and then go out, etc. this is something you just need to listen to when using two microphones on something.

there's a picture below that might help you

[raab]

So then is the trick to add a real small amount of delay to one mic to avoid phase cancellation?

[bennychico11]

no....the trick is to move the mics around until you don't hear any phase issues. always start at the source. however, you can also press the polarity switch (most boards or DAWs have them) on the channel to listen if it sounds better...this can help some of the times, but i'd say start at the source.